diff --git a/common.php b/common.php
index 69a85b0bc..73abee96f 100644
--- a/common.php
+++ b/common.php
@@ -54,7 +54,11 @@ if (!defined('IN_FORUM') && !defined('IN_TRACKER')) {
 header('X-Frame-Options: SAMEORIGIN');
 
 // Composer
-require_once(BB_ROOT . 'vendor/autoload.php');
+if (!file_exists(__DIR__ . '/vendor/autoload.php')) {
+    die('Please <a href="https://getcomposer.org/download/" target="_blank" rel="noreferrer" style="color:#0a25bb;">install composer</a> and run <code style="background:#222;color:#00e01f;padding:2px 6px;border-radius:3px;">composer install</code>');
+}
+
+require_once __DIR__ . '/vendor/autoload.php';
 
 // Get initial config
 require(BB_ROOT . 'library/config.php');